We previously described potent inhibition of Ebola virus entry by a ‘C-peptide’ based on the GP2 C-heptad repeat region (CHR) targeted to endosomes (‘Tat-Ebo’). Here, we report the synthesis and evaluation of C-peptides conjugated to cholesterol, and Tat-Ebo analogs containing covalent side chain–side chain crosslinks to promote a-helical conformation. We found that the cholesterol-conjugated C-peptides were potent inhibitors of Ebola virus glycoprotein (GP)-mediated cell entry (1000 -fold reduction in infection at 40 µM). However, this mechanism of inhibition is somewhat non-specific because the cholesterol-conjugated peptides also inhibited cell entry mediated by vesicular stomatitis virus glycoprotein G. One side chain–side chain crosslinked peptide had moderately higher activity than the parent compound TatEbo. Circular dichroism revealed that the cholesterol-conjugated peptides unexpectedly formed a strong a-helical conformation that was independent of concentration. Side chain–side chain crosslinking enhanced a-helical stability of the Tat-Ebo variants, but only at neutral pH. These result provide insight into mechanisms of C-peptide inhibiton of Ebola virus GP-mediated cell entry.